1. Field of the Invention
The present invention relates to an ink which is suitable for use in ink-jet recording, excellent in reliability, and capable of providing an image having a high optical density even on plain paper and also forming an image having excellent water fastness and resistance to line marker, and an ink set, ink cartridge, recording unit, image recording apparatus and image recording process using such an ink. The present invention also relates to an ink which is suitable for use in ink-jet recording, excellent in reliability, capable of providing an image having a high optical density even on plain paper, forming an image having excellent water fastness and resistance and further extremely effectively preventing bleeding at boundaries between different colors of a multi-color image on a recording medium when the multi-color image is formed together with other color inks by an ink-jet recording method, and an ink set, ink cartridge, recording unit, image recording apparatus and image recording process using such an ink.
2. Related Background Art
An ink-jet recording method is a system in which recording is conducted by ejecting an ink to apply the ink to a recording medium such as paper. According to an ink-jet recording system disclosed in, for example, Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914, in which an electrothermal converter is used as an ejection-energy supply means to apply thermal energy to an ink so as to generate bubbles, thereby ejecting the ink, the formation of a high-density multi-orifice in a recording head can be realized with ease, and a high-resolution and high-quality image can be recorded at high speed. Therefore, such an ink-jet system is a main system for ink-jet recording methods put to practical use at present.
By the way, for example, a water-soluble dye is used as a coloring material in an ink used in such an ink-jet recording method. However, images recorded with such an ink are required to more improve their water fastness, and resistance to line marker on plain paper.
When a multi-color printing is conducted on plain paper, there is also a demand for further reduction in the so-called color bleed caused by mixing of inks of different colors at boundaries between the inks in an image formed with such inks.
A great number of means for overcoming such problems, particularly, improving the optical density and water fastness of recorded images have been proposed to date. As one of the solutions thereof, it is proposed to prepare an ink containing a pigment as a coloring material and dispersed in water. For example, an ink using carbon black as a coloring material permits the provision of an image having a high optical density and excellent water fastness by ink-jet recording. However, such a recorded image still leaves room for improvement in rub-off resistance and resistance to line marker on plain paper in particular.
As a technique for overcoming such problems as described above, it has been known to improve image fixing ability by adding a resin in the ink. For example, Japanese Patent Application Laid-Open No. 3-172362 discloses a technique wherein a cationic emulsion, in which resin particles are dispersed as a fixing agent, is contained in an ink comprising a dye or pigment as a coloring material to improve the fixing ability of the ink on a recording medium. Japanese Patent Application Laid-Open No. 8-239610 discloses a water-based pigment composition for ink-jet, comprising a pigment, a colored resin and a humectant as essential components. It is also disclosed that a print excellent in both coloring ability and water fastness can be provided by such a composition.
According to the extensive study of the aforementioned prior art by the present inventor, since the upper limits of amounts of a pigment and a resin, which can be contained in an ink, are naturally defined when the ejection stability of the ink is taken into consideration, it is inevitable to choose the amount of the pigment, which affects the optical density of a recorded image, and the amount of the resin, which affects the image fixing ability of the ink, in terms of the balance between the trade-off characteristics, i.e., the optical density and the image fixing ability. Therefore, the present inventor has concluded that it cannot be yet said under the circumstances that the pigment inks proposed to date fully make the best use of merits obtained by using a pigment as a coloring material.
More specifically, Japanese Patent Application Laid-Open No. 8-239610 explains in the specification thereof that the colored resin is a dispersion of a resin colored by a dye. According to the preparation process of the colored resin described in the Example thereof, a dye is first added to an emulsion of a resin, and the mixture is heated to about 80xc2x0 C. and then cooled, thereby preparing the colored resin. However, in page 4, left column, lines 38 to 41 of this patent specification, it is described that xe2x80x9cIn order for the dye to be sufficiently taken in the resin, the amount (of the dye) is preferably 10 parts or less, particularly 8 parts or less, per 100 parts of the resinxe2x80x9d. In each of the preparation processes described in Preparation Examples 8 to 13 of the specification, a mixing proportion of the dye to the solid resin content in the emulsion polymer is described as about 1:10 to 1:12 (dye:resin). According to the investigation by the present inventor, it has however been concluded that, when such a colored resin as described in Japanese Patent Application Laid-Open No. 8-239610 is used, such a proportion of the dye to the resin as described in the specification may not be said in some cases to be sufficient to compensate for a reduction in an optical density, due to a reduction of amount of a coloring material which can be contained in an ink, accompanied by the addition of the resin to the pigment ink for the purpose of improving the fixing ability of the ink to recording media. Further, it is inferred that when the colored resin is intended to added to such an extent that a sufficient optical density is achieved, the colored resin must be added in such an amount that departs from a range in which an ink-jet ink can be precisely ejected by an ink-jet recording system. As described above, from the investigations as to the prior art, the present inventor has reached a conclusion that the development of a new technique entirely different from the conventional techniques is required for further improvements in optical density and image fixing ability in pigment inks.
Therefore, the present inventor has carried out a further investigation. As a result, a technique which can solve the problems on inks containing a pigment while making the best use of the merits obtained by using the pigment as a coloring material has been found, thus leading to completion of the present invention. Similarly, as the result of the investigation by the present inventors, a technique which can solve the problems on inks containing a pigment while making the best use of the merits obtained by using the pigment as a coloring material, and extremely effectively prevent bleeding when applied to multi-color printing has also been found, thus leading to completion of the present invention.
It is an object of the present invention to provide an ink which can provide an image high in optical density and excellent in rub-off resistance, water fastness and resistance to line marker, and exhibits excellent ejection stability from a recording head when used in ink-jet recording.
Another object of the present invention is to provide an ink which can provide an image high in optical density and excellent in rub-off resistance, water fastness and resistance to line marker, has excellent ejection stability from a recording head when used in ink-jet recording, and moreover can extremely effectively reduce bleeding when used in a multi-color printing.
A further object of the present invention is to provide an image recording process which can form an image high in optical density and excellent in rub-off resistance, water fastness and resistance to line marker.
A still further object of the present invention is to provide a multi-color image recording process which can form an image high in optical density and excellent in rub-off resistance, water fastness and resistance to line marker and moreover can extremely effectively reduce bleeding on a recording medium.
A yet still further object of the present invention is to provide an image recording apparatus which can be used in the stable formation of an image high in optical density and excellent in rub-off resistance, water fastness and resistance to line marker, and an ink set, an ink cartridge and a recording unit which can be used in such an image recording apparatus.
A yet still further object of the present invention is to provide an image recording apparatus which can be used in the stable formation of a multi-color image high in optical density, excellent in rub-off resistance, water fastness and resistance to line marker and extremely little in occurrence of bleeding, and an ink set, an ink cartridge and a recording unit which can be used in such an image recording apparatus.
The above objects can be achieved by the present invention described below.
In one embodiment of the present invention, there is thus provided an ink comprising a pigment and a resin encapsulating a coloring material.
Such an ink can provide a high-quality image high in optical density and excellent in rub-off resistance, water fastness and resistance to line marker by ink-jet recording, and is excellent in reliability (ejection durability, ejection stability, anti-clogging property, etc.) upon ink-jet recording.
In another embodiment of the present invention, there is provided an ink cartridge, comprising an ink container containing an ink, which comprises a pigment and a resin encapsulating a coloring material.
In a further embodiment of the present invention, there is provided a recording unit, comprising an ink container containing an ink, which comprises a pigment and a resin encapsulating a coloring material, a recording head and a means for feeding the ink from the ink container to the recording head.
In a still further embodiment of the present invention, there is provided an ink set comprising a first ink and a second ink in combination, wherein the first ink comprises a pigment and a resin encapsulating a coloring material, and each of the first and second inks has a color selected from the group consisting of yellow, magenta, cyan, black, red, green and blue.
In a yet still further embodiment of the present invention, there is provided an image recording process, comprising the step of applying an ink, which comprises a pigment and a resin encapsulating a coloring material, to a recording medium.
In a yet still further embodiment of the present invention, there is provided an image recording apparatus, comprising a recording unit which has an ink container containing an ink, which comprises a pigment and a resin encapsulating a coloring material, a recording head and a means for feeding the ink from the ink container to the recording head, and a means for actuating the recording unit to eject the ink from the recording head.
The above embodiments are adopted, thereby bringing about an effect that a high-quality image high in optical density and excellent in rub-off resistance, water fastness and resistance to line marker is provided by ink-jet recording.
In one embodiment of the present invention, there is provided an ink comprising either a pigment having a cationic group, or a pigment and a pigment dispersant having a cationic group, and a resin encapsulating a coloring material.
Such an ink can provide a high-quality image high in optical density and excellent in water fastness, resistance to line marker and rub-off resistance by ink-jet recording.
When a self-dispersing carbon black to the surface of which at least one cationic hydrophilic group is bonded directly or through another group is used as the pigment, the amount of a pigment dispersant or the like to be added into an ink can be reduced, or there need not add such a dispersant. As a result, reliability (ejection durability, ejection stability, anti-clogging property, etc.) upon ink-jet recording is also more improved in addition to the above-described effect.
In another embodiment of the present invention, there is provided an ink cartridge, comprising an ink container containing an ink, which comprises either a pigment having a cationic group, or a pigment and a pigment dispersant having a cationic group, and a resin encapsulating a coloring material.
In a further embodiment of the present invention, there is provided a recording unit, comprising an ink container containing an ink, which comprises either a pigment having a cationic group, or a pigment and a pigment dispersant having a cationic group, and a resin encapsulating a coloring material, a recording head and a means for feeding the ink from the ink container to the recording head.
In a still further embodiment of the present invention, there is provided an ink set comprising a first ink and a second ink in combination, wherein the first ink comprises either a pigment having a cationic group, or a pigment and a pigment dispersant having a cationic group, and a resin encapsulating a coloring material, and each of the first and second inks has a color selected from the group consisting of yellow, magenta, cyan, black, red, green and blue.
In a yet still further embodiment of the present invention, there is provided an image recording process, comprising the step of applying an ink, which comprises either a pigment having a cationic group, or a pigment and a pigment dispersant having a cationic group, and a resin encapsulating a coloring material, to a recording medium.
According to such an image recording process, there is brought about an effect that a high-quality image high in optical density and excellent in water fastness, resistance to line marker and rub-off resistance can be provided by ink-jet recording.
In a yet still further embodiment of the present invention, there is provided an image recording process, comprising the step of applying at least two color inks to a recording medium using an ink-jet recording method to form a multi-color image, wherein one ink comprises either a pigment having a cationic group, or a pigment and a pigment dispersant having a cationic group, and a resin encapsulating a coloring material, and the other ink comprises a compound having an anionic compound.
According to such an image recording process, a high-quality image high in optical density and excellent in water fastness, resistance to line marker and rub-off resistance can be provided by ink-jet recording, and a high-quality, multi-color image, which is reduced in occurrence of bleeding, can be formed by ink-jet recording.
In a yet still further embodiment of the present invention, there is provided an image recording apparatus, comprising a recording unit which has an ink container an ink, which comprises either a pigment having a cationic group, or a pigment and a pigment dispersant having a cationic group, and a resin encapsulating a coloring material, a recording head and a means for feeding the ink from the ink container to the recording head, and a means for actuating the recording unit to eject the ink from the recording head.
In a yet still further embodiment of the present invention, there is provided an image recording apparatus, comprising a recording unit which has ink containers containing first and second inks respectively, a recording head and a means for feeding the inks from the ink containers to the recording head, and a means for actuating the recording unit to eject the respective inks from the recording head, wherein the first ink comprises either a pigment having a cationic group, or a pigment and a pigment dispersant having a cationic group, and a resin encapsulating a coloring material, and the second ink is an anionic ink.
According to such an image recording apparatus, a high-quality image high in optical density and excellent in water fastness, resistance to line marker and rub-off resistance can be provided by ink-jet recording, and a high-quality, multi-color image, which is reduced in occurrence of bleeding, can be formed by ink-jet recording.